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PubMedDate not supplied

Measurement of the symmetry of in vitro stent expansion: a stereo-photogrammetric approach.

Balloon-expandable stents are used routinely in the treatment of coronary artery disease. Their effectiveness is limited by the occurrence of restenosis. Previous studies have suggested that the level of restenosis may be related to the deployed stent geometry, and in particular to the symmetry of the deployment profile. It is suggested that the symmetry of deployment might be influenced by the folding pattern of the balloon on which the stent is delivered. This paper describes a stereo-photogrammetric system for the three-dimensional reconstruction of stent geometry during expansion, including appropriate specification and calibration procedures. Calibration testing of the system indicated an accuracy of +/-0.05 mm in the reconstruction of the position of a point on the stent surface. Methods for processing the 3D data are described, including a technique for quantitatively differentiating between results from two alternative balloon folding patterns. This study may aid future balloon and stent design with respect to the optimization of stent deployment characteristics.

Biomechanical Phenomena↗

PubMed2006

Rationalizing foot and ankle measurements to conform to a rigid body model.

Accurate estimation of the in vivo locations of skeletal landmarks plays an integral role in several biomechanical research techniques. Because of rounding errors caused by instruments or skin movement, the data obtained through cinematography are usually not accurate and rise to a distance matrix which, because of the data errors, may not be Euclidean. The aim of this paper is to find the best Euclidean distance matrix (EDM) that approximates the distance matrix and then, an accurate estimation of the locations of skeletal landmarks. A useful scheme for parametrizing an orthogonal matrix is also described.

Algorithms↗

PubMedDate not supplied

The practical use of surface topography: following up patients with Scheuermann's disease.

PURPOSE: The purpose of this study was to answer the question of whether a course of in-patient rehabilitation of 4-6 weeks results in a significant postural improvement in patients with a structural kyphosis. Since all clinical measuring parameters are liable to high margins of error and measuring the surface with the formetric system has shown high reliability in previous studies, this system has been used to evaluate the results of rehabilitation in patients with Scheuermann's disease. MATERIALS AND METHOD: A pre-/post-interventional study was undertaken including only patients (n = 136) with Scheuermann's kyphosis and a thoracic curve pattern. 62 female patients with an average age of 19 years and 74 male patients of average age 20 years were diagnosed with the Formetric system before an in-patient rehabilitation programme of 4-6 weeks. For this study, the maximal kyphotic angle was evaluated. RESULTS: The average kyphotic angle as measured by the surface topography system before inpatient rehabilitation was 60.7 degrees (SD 11.2) and after 54.9 degrees (SD 12.1) for the whole sample of 136 patients. The improvements where highly significant in the t-test. In the cases of the female patients, the maximal kyphotic angle decreased from 62 degrees to nearly 54 degrees; in the cases of the male patients it had decreased from 60 degrees to nearly 55 degrees by the end of the programme. DISCUSSION: After the in-patient treatment, the kyphotic angle decreased very significantly. The range of change was far greater than the margin of error and, thus, the following conclusion may be reached: In-patient rehabilitation with an intensive programme of treatment may result in a correction of structural kyphoses in which there are clear signs of Scheuermann's disease. Consequently in-patient rehabilitation is recommended for adolescents in cases of Scheuermann's kyphoses.

Adult↗

PubMed2004

Stereo-assisted landmark detection for the analysis of changes in 3-D facial shape.

In this paper, a semi-automated approach to 3-D landmark digitization of the face is described which uses a combination of active shape model-driven feature detection and stereophotogrammetric analysis. The study aims to assess whether the proposed method is capable of detecting statistically significant changes in facial soft tissue shape due to mandibular repositioning in a cross-sectional patient sample. A hybrid stereophotogrammetric and structured-light imaging system is used for acquiring 3-D face models in the first instance. A landmark-based statistical analysis of facial shape change is then carried out using procrustes registration, principal component analysis and thin plate spline warping on the 2-D facial midline profiles and automatically digitized 3-D landmarks. The proposed method is validated both statistically and visually by characterizing shape changes induced by mandibular repositioning in a heterogeneous cross-sample of 20 orthodontic patients. It is shown that the method is capable of distinguishing between changes in facial morphology due to simulated surgical correction and changes due to other factors such as growth and normal variation within the patient sample. The study shows that the proposed method may be useful for auditing outcomes of clinical treatment or surgical intervention which result in changes to facial soft tissue morphology.

Adolescent↗

PubMed2006

Effects of light refraction on the accuracy of camera calibration and reconstruction in underwater motion analysis.

One of the most serious obstacles to accurate quantification of the underwater motion of a swimmer's body is image deformation caused by refraction. Refraction occurs at the water-air interface plane (glass) owing to the density difference. Camera calibration-reconstruction algorithms commonly used in aquatic research do not have the capability to correct this refraction-induced nonlinear image deformation and produce large reconstruction errors. The aim of this paper is to provide a thorough review of: the nature of the refraction-induced image deformation and its behaviour in underwater object-space plane reconstruction; the intrinsic shortcomings of the Direct Linear Transformation (DLT) method in underwater motion analysis; experimental conditions that interact with refraction; and alternative algorithms and strategies that can be used to improve the calibration-reconstruction accuracy. Although it is impossible to remove the refraction error completely in conventional camera calibration-reconstruction methods, it is possible to improve the accuracy to some extent by manipulating experimental conditions or calibration frame characteristics. Alternative algorithms, such as the localized DLT and the double-plane method are also available for error reduction. The ultimate solution for the refraction problem is to develop underwater camera calibration and reconstruction algorithms that have the capability to correct refraction.

Algorithms↗

PubMed2005

Guidelines for standardization of radiostereometry (RSA) of implants.

There is a need for standardization of radiostereometric (RSA) investigations to facilitate comparison of outcome reported from different research groups. In this document, 6 research centers have agreed upon standards for terminology, description and use of RSA arrangement including radiographic set-up and techniques. Consensus regarding minimum requirements for marker stability and scatter, choice of coordinate systems, and preferred way of describing prosthetic micromotion is of special interest. Some notes on data interpretation are also presented. Validation of RSA should be standardized by preparation of protocols for assessment of accuracy and precision. Practical issues related to loading of the joint by weight bearing or other conditions, follow-up intervals, length of follow-up, radiation dose, and the exclusion of patients due to technical errors are considered. Finally, we present a checklist of standardized output that should be included in any clinical RSA paper.This document will form the basis of a detailed standardization protocol under supervision of ISO and the European Standards Working Group on Joint Replacement Implants (CEN/TC 285/WG4). This protocol will facilitate inclusion of RSA in a standard protocol for implant testing before it is released for general use. Such a protocol-also including other recognized clinical outcome parameters-will reduce the risk of implanting potentially inferior prostheses on a large scale.

Arthroplasty, Replacement, Hip↗

PubMed2005

Radiostereometric analysis of the double-coated STAR total ankle prosthesis: a 3-5 year follow-up of 5 cases with rheumatoid arthritis and 5 cases with osteoarthrosis.

BACKGROUND: The designs of total ankle prostheses have changed in recent years in order to give better performance. Only a few studies of these ankle prostheses have been published, however, and none on micromotion. PATIENTS AND METHODS: We evaluated 5 patients with rheumatoid arthritis and 5 with osteoarthrosis, 4 (3-5) years after arthroplasty with the double-coated STAR prosthesis. Clinical examination included AOFAS hindfoot score. Standardized a-p and lateral radiographs were taken and RSA analyses were done at regular intervals. RESULTS: There was no difference in results between ankles operated on due to rheumatoid arthritis and due to osteoarthrosis. A rapid initial migration was observed for the tibial components at 6 weeks, but thereafter all but 1 implant seemed stable. The migration pattern for the talar component was similar. Rotation around the 3 axes was observed for the tibial components at 6 weeks, but not thereafter. The talar components became stable for rotation around the longitudinal and sagittal axes, but not around the transverse axis. 8 out of 10 ankles were painless. The median total AOFAS score was 83 and the median range of motion was 32 degrees. None of the 20 components had changed position and there were no signs of bone resorption. INTERPRETATION: Provided the indication is adequate and the prosthesis has been implanted correctly, the double-coated STAR ankle prosthesis will have a satisfactory fixation to underlying bone.

Ankle Joint↗

PubMed2005

Kinematics before and after reconstruction of the anterior syndesmosis of the ankle: A prospective radiostereometric and clinical study in 5 patients.

BACKGROUND: We have previously shown that patients with instability of the anterior syndesmosis benefit from an anatomical reconstruction. It is not known whether this is because of restored kinematics. METHODS: In a prospective study of 5 patients, we assessed clinical findings and tibiofibular kinematics, evaluated by radiostereometry, before and after reconstruction of a chronic syndesmotic injury. RESULTS: We found no statistically significant differences in tibiofibular kinematics before and after reconstruction. The kinematics of the fibula relative to the tibia during external rotation stress differed from that known in asymptomatic volunteers, but the differences were not typical enough to differentiate between patients and healthy subjects. Clinical examination and ankle scores, however, showed that all patients benefited from reconstruction of the anterior syndesmosis. INTERPRETATION: Radiostereometry is not an adequate technique to diagnose chronic syndesmotic instability or to demonstrate restoration of the kinematics of the ankle as a cause of the beneficial effect of anatomical reconstruction of the syndesmosis.

Adult↗

PubMed2006

Stepwise introduction of a bone-conserving osseointegrated hip arthroplasty using RSA and a randomized study: I. Preliminary investigations--52 patients followed for 3 years.

BACKGROUND: We developed a total hip system using osseointegration guidelines, a metaphyseal-loading proximal femoral replacement in the retained neck and a dual-geometry titanium shell in the acetabulum. PATIENTS AND METHODS: A randomized controlled clinical trial was undertaken in 52 patients (53 hips), using the cemented Spectron stem and cementless Harris-Galante II cup as control implants (24 patients in experimental group, 29 control patients). Clinical measures of Harris Hip Score (HHS), pain score and radiostereometric analysis (RSA) at regular intervals for up to three years were used to monitor progress. RESULTS: No statistically significant differences were found in HHS and pain score; the stability of the cementless experimental implant was also comparable to that of the cemented controls by RSA. 3 revisions were required for migration in the experimental group and 1 was required for component dislocation in the control group. INTERPRETATION: Our findings indicate the practicality of osseointegration of titanium implants, but suggest that current performance is inadequate for clinical introduction. However, the stable fixation achieved in the retained neck in the majority of patients is indicative of osseointegration. This finding will encourage technical and design improvements for enhancement of clinical osseointegration and should also encourage further study. Periprosthetic osteolysis might be avoided by the establishment and maintenance of direct implant-bone connection: "osseointegration".

Acetabulum↗

PubMed2006

Stepwise introduction of a bone-conserving osseointegrated hip arthroplasty using RSA and a randomized study: II. Clinical proof of concept--40 patients followed for 2 years.

BACKGROUND: We have developed a bone-conserving commercially pure titanium hip replacement system using osseointegration principles: a metaphyseal loading proximal femoral component affixing into the retained neck and metaphysis only, leaving the femoral canal untouched. The acetabular cup closely fits a dual-geometry cavity, avoiding stress protection at the dome. PATIENTS AND METHODS: After extensive laboratory and clinical pilot trial investigations, the surface-engineered implants were submitted to a prospective randomized controlled clinical trial involving 40 patients (40 hips), in which they were compared to the cemented Spectron femoral component and cementless Trilogy cup as control implant. The following clinical measures were used to monitor progress at regular intervals for the first 2 postoperative years: radiostereometric analysis (RSA), Harris Hip Score, pain score, WOMAC, and SF-36. RESULTS: After 2 years of follow-up, no statistically significant differences were seen between the groups concerning rotation or translation along the cardinal axes. The patients receiving the Gothenburg osseointegrated titanium (GOT) system had significantly higher Harris Hip Score at 6 months, suggesting more rapid recovery. WOMAC, SF-36 and pain analysis were similar for the first 2 postoperative years. INTERPRETATION: Our RSA data suggest that osseointegration was achieved for all patients receiving the GOT hip system. This bone-conserving prosthesis may provide a good alternative, especially for young and active patients.

Acetabulum↗

PubMed2006

Comparison of the uncemented Cone and the cemented Bimetric hip prosthesis in young patients with osteoarthritis: an RSA, clinical and radiographic study.

BACKGROUND: There is no consensus as to whether uncemented or cemented femoral stems should be used in younger patients. We compared the uncemented Cone stem to the cemented Bimetric stem in young patients with osteoarthritis. PATIENTS AND METHODS: We randomized 45 relatively young patients (< 65 years old, mean age 54 years) with osteoarthritis to either an uncemented Cone stem or a cemented Bimetric stem. All patients were followed for 2 years. Outcome was assessed by the Merle d'Aubigné score, conventional radiography and repeated radio-stereometric analysis (RSA). We also followed 81 Cone stems for 8 (7-12) years with revision as endpoint. RESULTS: The clinical outcome was excellent. No patient had postoperative thigh pain. The migration was small. The Bimetric stem was stable during the whole observation period, while the Cone stem subsided and rotated to retroversion during the first 3 months post-operatively, and then remained stable. In the follow-up study of 81 Cone stems, 1 stem was revised. INTERPRETATION: We conclude that both the cemented Bimetric stem and the uncemented Cone stem are stable and give excellent clinical results after 2 years in relatively young patients with osteoarthritis. Although designed for CDH hips, the Cone stem appears to be suitable also for patients with osteoarthitis.

Adult↗

PubMed2006

Weight bearing radiographs are not necessary for measurement of polyethylene penetration in total hip prostheses: a radiostereometric study of 111 patients examined in weight-bearing and supine position.

BACKGROUND: Controversy exists as to whether polyethylene (PE) penetration of hip prostheses is underestimated when the measurements are made on radiographs obtained in supine position as compared to weight-bearing position. PATIENTS AND METHODS: We examined 111 patients by radiostereometric analysis (RSA) in the supine and weight-bearing positions. RESULTS: The mean 3-D penetration was 0.68 mm (SD 0.58, range 0.04-3.05) for the supine position and 0.70 mm (SD 0.57, range 0.08-3.01) for the weight-bearing position. The correlation between supine and weight-bearing examinations was 0.99 (p < 0.001). The degree of penetration made no difference. There was no statistically significant difference as to whether the first examination was performed early, i.e. after 3 months, or after 12 months (p = 0.7). INTERPRETATION: The small systematic difference in penetration values between the supine and the weight-bearing positions is of no clinical or methodological importance.

Arthroplasty, Replacement, Hip↗

PubMed1988

Active knee motion after cruciate ligament rupture. Stereoradiography.

In 10 patients with an old injury of the anterior cruciate ligament, the three-dimensional movements of the knee joint were studied when the patients flexed their knees. Tibial motions were recorded using roentgen stereophotogrammetric analysis. Internal rotation and adduction of the tibia were reduced in the injured knees when compared with the intact knees; during flexion of the knee joint, the tibial intercondylar eminence occupied a more lateral and posterior position on the injured side. Our results may indicate that the knee joint is continuously exposed to abnormal stresses when the anterior cruciate ligament is torn.

Adult↗

PubMed1992

Lengthening of anterior cruciate ligament graft. Roentgen stereophotogrammetry of 32 cases 2 years after repair.

32 patients with old anterior cruciate ligament injuries were operated on with patellar tendon-prepatellar tissue-quadriceps tendon graft over the top without and with augmentation (Kennedy-LAD). The anteroposterior (AP) laxity was assessed preoperatively, and at 6, 12, and 24 months after the operation with roentgen stereophotogrammetry. 6 months postoperatively the instability had decreased 5.4 mm in the nonaugmented and 1.9 mm in the augmented group, but not to normal values. During the following 18 months the AP laxity increased and returned to the preoperative level. At 2 years, 28 of the 32 patients were considered good or excellent, according to the Lysholm score. There was a lack of correlation between AP laxity and functional tests.

Adult↗

PubMed1992

Instability after anterior cruciate ligament rupture. Measurements of sagittal laxity compared in 11 cases.

Manual tests and 2 external devices were used together with roentgen stereophotogrammetry (RSA) and an active weight-bearing radiographic method to measure the sagittal laxity in 11 knees with anterior-cruciate-ligament rupture. In 5 knees no ligament surgery had been performed (unstable knees) and in 6 knees a reconstruction had been performed one year before the examination (stable knees). There were positive correlations between all methods, including the manual tests when all knees, both stable and unstable, were analyzed together. However, the mean values of the total displacement differed between the methods, especially when comparing the weight-bearing radiographs with the three other methods. Some knees with substantial displacement during passive loading did not show any displacement when weight bearing; the measurements thus depended on both the ligamentous laxity and the patient's neuromuscular control of the joint. When the stable knees were analyzed separately, higher mean values were recorded with the external devices than with RSA using 180 N load. This could be explained by an error from soft tissue deformation which added to the skeletal displacement when the external devices were used.

Adolescent↗

PubMed1978

A computer driven photoscanner for medical imaging.

A novel and versatile instrument for producing high quality monochrome and colour hard-copy of medical images from an array of digital information is described. Images are produced on standard photographic print paper mounted on the bed of a conventional X-Y plotter by scanning a time-modulated light source over the paper using a computer driven raster. A matrix board gives control of both greyscale and colour attribution. Examples of NMR images produced by the system are presented. A refinement of the technique which allows two variables to be displayed on one image is also described.

Color↗

PubMed1979

Theoretical aspects and practical applications of moiré topography.

When a surface is observed at a distance through a parallel line grating which is illuminated by a source of light laterally displaced to the viewing axis, the grating is superimposed on its shadow and this gives rise to a moiré fringe pattern. The fringes represent cross-sections of the surface parallel to the grating plane. The principle of the formation of the contour map has been studied assuming a grating represented by a Fourier series, a source of light represented by a 3D intensity distribution and a viewing aperture of finite dimensions. The experimental system used for illumination and observation of the moiré fringes consists of an equispaced parallel-lined glass grating and two small light sources positioned symmetrically about the imaging device. The arrangement constitutes a 3D imaging system with an accuracy of the order of 1 mm. The technique has been applied in radiotherapy problems such as the design of contour compensators and the measurement of body contours. Moiré patterns have been analysed with the aid of a PDP-8 computer, and have been used to calculate surface areas and volumes such as in breast studies and superficial tumour measurements.

Humans↗

PubMed1979

Evaluation of a moiré imaging system.

Moiré fringe techniques can be used to measure surface topography. The factors that affect the formation of the fringes have been assessed theoretically by developing models of gratings and light sources of finite dimensions. In this way the effect of parameters such as the intensity distribution of the light source, the viewing aperture function, the lateral displacement of the source relative to the viewing axis, the viewing distance, the grating spacing and grating ratio have been evaluated. Other factors, related to the physical properties and geometry of the reflecting surface, are also investigated. Suggestions are made for the design of an optimum moiré imaging system.

Interferometry↗